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Re: [Xen-devel] [PATCH] xen: do not unmask disabled IRQ on eoi.

To: "Stefano Stabellini" <stefano.stabellini@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] xen: do not unmask disabled IRQ on eoi.
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 19 Oct 2010 07:36:19 +0100
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "jeremy@xxxxxxxx" <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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>>> On 18.10.10 at 20:14, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> 
>>> wrote:
> On Mon, 18 Oct 2010, Jan Beulich wrote:
> The other type of pirqs are the ones that have ack_type != ACKTYPE_NONE,
> in these cases xen waits for the guest to issue the eoi before acking
> the machine irq so it shouldn't be possible to receive any pirqs while
> we are handling the first one.

But even in that case you do the clear after the EOI notification, i.e.
you still have a window where you may lose an event.

> That said, I don't see any simple way to improve this patch so that we
> are able to receive one notification while handling a pirq without
> changing the semantic of the fasteoi handler or switching to the edge
> handler for pirqs that don't need eoi.

What I'm trying to say is that I think the direct mask/clear in do_upcall()
should stay as it is.


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